RPG Theory Glossary: U

A term coined by Ron Edwards on The Forge for a technique of
preparation and play using a canonical setting and storyline,
known to all participants, in which the events of play create
a "hidden" storyline to enrich and reinforce the primary one,
which is treated as a creative constraint. Also called
"inverse metaplot."
References:
Metaplots, railroading, and settings
Open/closed setting (Pyron's woes take 165)

Universal

General term for an RPG system intended for multiple settings. The
difference between a "universal system" (like GURPS) and a "house system"
(like Storyteller) is largely one of publishing -- i.e. do you publish
core rules and then modifications to those, or do you publish tailored
rule sets with the modifications already applied? This can be a
controversial topic on The Forge.
References:
universal vs specific systems
General views on Universal systems?